Background: Pulmonary sarcomatoid carcinoma is a rare, poorly differentiated, and highly aggressive type of non-small cell lung cancer. High tumor mutational burden and PD-L1 overexpression make it an excellent candidate for immunotherapy. Objectives and Method: We presented the case of a patient who underwent left inferior lobectomy with concurrent right paravertebral muscular metastasectomy for an infiltrative neoplastic mass, whose final diagnosis was consistent with stage IV pulmonary sarcomatoid carcinoma. He received first- and second-line chemotherapy without any benefit. Since March 2016, he has been treated with the anti-PD1 agent nivolumab with a dramatic improvement of symptoms, disappearance of a brain lesion, and partial response on other metastatic sites. He tolerated the treatment well and is still responding after 22 months from the beginning. Results and Conclusions: In very lethal non-small cell lung cancer subtypes such as the sarcomatoid variants, high tumor burden and deteriorated general conditions should not preclude, at least in some cases, the use of immunotherapy. Anti-PD1 may also have a reliable role in disease control in the brain. Lastly, the strong rationale behind sarcomatoid histology should further prompt trials exploring immunotherapeutic approaches in this subset of non-small cell lung cancer.